This paper presents a systematic review of cloud security issues and existing methodologies proposed by researchers. It summarizes 15 previous studies that proposed algorithms or approaches for cloud security. For each study, it provides the proposed approach, pros, and cons. Some key approaches included single sign-on, data partitioning, role-based access control, encryption algorithms, hashing techniques, and fault tolerance schemes. Overall, the paper surveys cloud security challenges and reviews prior work to address issues like authentication, authorization, data integrity, and reliability.